Presentation on theme: "Riparian Management and Fish Productivity Peggy Wilzbach and Ken Cummins USGS CA Cooperative Fish Research Unit Humboldt State University."— Presentation transcript:
Riparian Management and Fish Productivity Peggy Wilzbach and Ken Cummins USGS CA Cooperative Fish Research Unit Humboldt State University
Habitat isn’t enough. Fish need food! Many streams with pristine habitat support low production of salmonid fishes Some of the most productive streams have suboptimal habitat (but abundant food) The greatest salmonid production is realized in hatchery channels!
Options for increasing salmonid production? Direct addition of food organisms (not realistic over long-term) Nutrient or organic matter enrichment Increasing autotrophic production
Case study: Effects of riparian canopy opening and salmon carcass addition on the abundance and growth of resident salmonids Wilzbach, M.A. et al. 2005. Can. J. Fish. Aquat. Sci. 62: 1-10.
Conclusions: Increased light was more effective than carcass addition in enhancing salmonid productivity of study sites Carcass enhancement may fail to increase salmonid production in settings where light is limiting or other factors prevent its successful use Selective trimming of riparian alder should be evaluated as a management tool for enhancing salmonid production
Can the food-generating capacity of a stream be readily assessed? Across broad spatial scales, highly productive streams are associated with: moderate temperatures, groundwater inputs relatively low vegetative canopy coverage hard waters, relatively high concentrations of inorganic nutrients
Within regions, need to directly measure prey availability Macroinvertebrate drift more accurately reflects prey availability than does the benthos The ratio of behavioral to accidental drifters may provide a good index of prey availability during low flow conditions
Behavioral drifter: predictably available on a diel basis Accidental drifter: without predictable pattern of drift entry; “windfall” diet items
Percent of drift mass from behavioral drifters (ASIN SQRT) Specific growth rate of salmonids (% · day -1 ) R 2 = 0.42 Summer
Percent of Terrestrial Invertebrates in Drift (ASIN SQRT) Specific growth rate of salmonids (%· day -1 ) R 2 = 0.62 In our study, % of terrestrial inverts was negatively related to fish growth
to establish the amount, spatial pattern of light gain, and riparian composition needed to optimize local food supplies - without sacrificing beneficial functions of riparian vegetation or cumulating temperature loadings downstream. Research needs: